A conventional television receiver, such as a receiver in accordance with NTSC broadcast standards adopted in the United States and elsewhere, has a 4.times.3 image aspect ratio (the ratio of the width to the height of a displayed image). Recently, there has been interest in using higher aspect ratios for television systems, such as 5.times.3 or 16.times.9, since such higher aspect ratios more nearly approximate or equal the aspect ratio of the human eye than does the 4.times.3 aspect ratio of a conventional television display system.
One advantageous 5.times.3 aspect ratio widescreen television system, incorporating additional detail information to provide extended image definition, is described in U.S. Pat. No. 4,855,811--Isnardi. In that system, side panel image information and extended definition image information are encoded to provide an extended definition widescreen television signal which is compatible with pre-existing standard aspect ratio (4.times.3) television receivers. More specifically, high frequency side panel information and extended definition information are encoded by modulating a phase controlled auxiliary subcarrier associated with a first signal component. Low frequency side panel information is encoded by time compressing such information into a horizontal overscan region of main panel information, associated with a second signal component. The first and second signal components are combined to form an encoded NTSC compatible television signal which is transmitted to a receiver.
The input circuits of the receiver include an averager-differencer network which separates the first and second components of the NTSC compatible signal. The averager-differencer network includes a plurality of field memory devices, a low pass filter, and an adder for combining high frequency main panel luminance information and low frequency main panel luminance information to reconstitute a main panel image. Each of the field memories is a costly device, and the low pass filter requires a precise filtering characteristic with a sharp cut-off. In addition, the signals combined by the adder should exhibit precise synchronism. Apparatus according to the present invention advantageously eliminates the need for such low pass filter and adder, requires fewer field memory devices, and includes provision for separating the luminance and chrominance components of a color television signal.